C major is enharmonic with B♯ Major with 12 sharps and Dbb Major with 12 flats (both alternatives are impractical though), so let's just call it C major!
Such a key only exists in theory. C major has zero flats. C-flat major has 7 flats. C-double-flat major would have 14 flats.
Such a key only exists in theory and not in practice. In C-double-flat major, every single note (C D E F G A B C) would have a double-flat on it, and it would sound the same as B-flat major.
The relative major key of C minor is E flat major.
The relative major of the key of C minor is E flat major.
The key signature of the F flat major key has six flats: B flat, E flat, A flat, D flat, G flat, and C flat.
The Keys of B-flat, E-Flat, A-Flat, D-Flat, G-Flat, C-Flat, and F-Flat major all contain the note E-flat. F-flat major is a key which only exists in theory and not in practice, since there is a double flat in that scale (subdominant). The major scale with the most flats is C-flat major - with all seven flats.
The chords in the key of E flat major are E flat major, F minor, G minor, A flat major, B flat major, C minor, and D diminished.
The chord symbol for a dominant 7 flat 9 in the key of C major is C7b9.
The key signature of a piece written in F flat major has six flats: B flat, E flat, A flat, D flat, G flat, and C flat.
The key signature with three flat signs is E-flat major. It contains the notes E-flat, F, G, A-flat, B-flat, C, and D. The relative minor of E-flat major is C minor, which also shares the same key signature.
F major: F G A Bb C D E F B is flat
15 different key signatures exist. (no sharps or flats) = C major F sharp= G major F C sharp = D major F C G sharp = A major F C G D sharp = E major F C G D A sharp = B major F C G D A E sharp = F # major F C G D A E B sharp = C# major B E A D G C F flat = C flat major B E A D G C flat = G flat major B E A D G flat = D flat major B E A D flat = A flat major B E A flat =E flat major B E flat =B flat major B flat = F major